Altering natural photosynthesis through quantum dots: effect of quantum dots on viability, light harvesting capacity and growth of photosynthetic organisms.

Quantum dots are versatile fluorescent semiconductor nanocrystals with unique photophysical properties. They have been used in various research fields of biotechnology effectively for almost three decades including cell imaging, protein tracking, energy transfer, etc. With their great potential as energy donors or acceptors, quantum dots have also been used in many studies about altering growth rate and photosynthetic activity of photosynthetic organisms by manipulating their light harvesting capacity. In this review, effect of quantum dots on growth rate of photosynthetic organisms and light harvesting capacity of photosynthetic organisms were discussed in details together with toxic effects of cadmium-based and carbon-based quantum dots on photosynthetic organisms. In short, as one of the promising materials of nanotechnology, quantum dots have become one of the essential research topics in photosynthesis research area and will help researchers to manipulate natural photosynthesis in future.

Effect of heteroatom-doped carbon quantum dots on the red emission of metal-conjugated phthalocyanines through hybridization.

Quantum dots (QDs) are significant fluorescent materials for energy transfer studies with phthalocyanines (Pcs) and phthalocyanine (Pc)-like biomolecules (such as chlorophylls). Carbon-based QDs, especially, have been used in numerous studies concerning energy transfer with chlorophylls, but the numbers of studies concerning energy transfer between phthalocyanines and carbon-based QDs are limited. In this study, peripherally, hydroxythioethyl terminal group substituted metal-free phthalocyanine (H2 Pc) and zinc phthalocyanine (ZnPc) were noncovalently (electrostatic and/or π-π interaction) attached to carbon QDs containing boron and nitrogen to form QD-Pc nanoconjugates. The QD-Pc conjugates were characterized using different spectroscopic techniques (Fourier transform infrared spectroscopy and transmission electron microscopy). The absorption and fluorescence properties of QD-Pc structures in solution were studied. It was found that the quantum yields of the QDs slightly decreased from 30% to 25% upon doping the QDs with heteroatoms B and N. Förster resonance energy transfer efficiency was calculated as 33% for BCN-QD/ZnPc. For the other conjugates, almost no energy transfer from QDs to Pc cores was observed. It was shown that the energy transfer between QDs to Pc cores was completely different from the energy transfer between QDs and photosynthetic pigments, and therefore we concluded that heteroatom doping in the QD structure and the existence of zinc metal in the phthalocyanine structure is obligatory for an efficient energy transfer.

Enhanced fluorescence of photosynthetic pigments through conjugation with carbon quantum dots.

Light harvesting in photosynthesis is currently an issue on-debate and studied widely in all over the world. Studies on light harvesting mainly focus on enlightening molecular mechanism of the process and enhancing absorption capacity of light harvesting complexes (LHCs). Enhancement of absorption capacity of LHCs can be done either by natural methods or by synthetic methods. Quantum dots (QDs), fluorescent semiconductor nanocrystals, are important constituents of inorganic-organic hybrid structures which are built to enhance absorption capacity of LHCs through synthetic methods. In this study, we synthesized carbon and heteroatom doped carbon QDs through a microwave assisted synthesis method. Each QD had unique photophysical and structural properties. Photosynthetic pigments (PP) (isolated from spinach leaves) were mixed with each QD separately to build a QD-PP hybrid structure. Our results revealed that significant amount of energy is transferred from carbon QDs to PPs and therefore chlorophyll fluorescence capacity of PPs enhanced significantly in 360-420 nm excitation wavelength interval. Our results suggested that non-toxic, inexpensive and easily synthesized carbon QDs can be an important constituent for hybrid structures to enhance absorption capacity of LHCs in highly energetic region of visible spectrum.